A NAND-type flash memory has been well known. In the NAND-type flash memory, a block with a state of data erasure is searched in a specific timing. An erasure block search is performed before writing data into a memory cell, for example. Further, data is written into the erased block found in the search.
Searching the erased block is generally performed by using reading out in general. Specifically, a top page of each block to be searched is read out, and the searched area is all the blocks for user data in the memory, for example.
When the top page is set to be the erasure state, the block including the page is determined to be the erasure state, for example. Generally, reading out data includes pre-charging all bits in the memory.
On the other hand, a page size is increased with higher integration of the NAND-type flash memory. Increase of the page size leads to increase of a number of the memory cell. Accordingly, a number of the bit lines are also increased.
In such a manner, electrical current in pre-charging the bit lines of reading out data is increased. Therefore, electrical current used in the block search is also increased.